[Bug] Systemic JMD currency precision failures — float amounts, wrong tx history, 100× inflation, hardcoded USD

[islandbitcoin]

Unified tracking issue for JMD currency precision failures (Mobile)

GitHub Issue: #555

14 distinct bugs across backend + mobile. This issue tracks the mobile fixes.

Supersedes: ENG-81, ENG-87

Depends on: ENG-132 (backend fixes must land first for Wave 1)

PR Review: Nick must approve before merge. Dread (islandbitcoin) final sign-off.

[linear]

ENG-133

[islandbitcoin]

Companion backend issue: lnflash/flash#282